Remove the use of the FV3 sigma pressure hybrid coordinate "ak" and "bk" coefficients in the UGWP scheme

[mdtoyNOAA]

Description

The three modules that call the non-stationary gravity wave drag (NGWD) schemes of the UGWP, cires_ugwp.F90, unified_ugwp.F90 and ugwpv1_gsldrag.F90, explicitely use the FV3 sigma-pressure hybrid-coordinate coefficients "ak" and "bk" to determine the "launch level" for non-stationary gravity waves. This prevents the CCPP-physics library from being "agnostic" to the host dynamical core, as not all dycores use this vertical coordinate system.

Solution

The goal would be to find a solution that reproduces identical results to the current code. No such solution has been found yet. A compromise may be to have results that are "close enough" to those of the current code.